Already recognised as the oldest person in the world, Mrs Okawa will on March 5 reach the remarkable milestone of 116 - and attributes her longevity to eating well and sleeping at least eight hours every night, with the occasional nap thrown in for good measure.

“Eat and sleep and you will live a long time,” she said in a message to The Telegraph. “You have to learn to relax.”

The daughter of a kimono-maker from Japan’s second city, Mrs Okawa assumed the title of the oldest person in the world after the death of 116-year-old Jireomon Kimura in June 2013.

Experts say it is no coincidence that both record-holders are from Japan, which was home to 54,397 centenarians on the last Respect for the Aged national holiday in September - including 282 super-centenarians, who have achieved the ripe old age of 110.

“Mrs Okawa eats three large meals a day and makes sure that she sleeps eight hours a night,” said Tomohito Okada, the head of the Kurenai retirement home where she has lived for the last 18 years.

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“She insists that her favourite meal is sushi, particularly mackerel on vinegar-steamed rice, and she has it at least once every month,” he said.

Asked about the happiest moments of a life that has now spanned three centuries, Mrs. Okawa unhesitatingly recalls her marriage in 1919 to Yukio Okawa and the birth of their three children. Her surviving son and daughter have clearly inherited her genes and are now aged 94 and 92.

She also has four grandchildren and six great-grandchildren.

Equally, she says the saddest time of her life was the death of her husband in June 1931 - an almost unthinkable 83 years ago.

The average lifespan for a Japanese woman is now 85.9 years, with women also accounting for 87 percent of the nation’s centenarians. A Japanese man can expect to reach 79.6 years old.

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Experts put Japanese longevity down to the nation’s comprehensive healthcare system, the support of the community, encouragement to remain physically active until they are quite elderly, a sense of being part of a family and a healthy diet that has traditionally been heavy in fish, rice, vegetables and fruit.

Additional research has suggested that people who were in middle-age during the years of food shortages during the Second World War have subsequently enjoyed better long-term health than people who never had to go without.

But Yasuyuki Gondo, an associate professor at Osaka University who specialises in geriatric psychology, says there is much more to longevity than merely a good diet and advanced medical care.

“When we surveyed centenarians, we found that the majority have enjoyed good mental health throughout their lives and have developed psychological adaptations to their situations as they have got older,” he told The Telegraph.

Professor Gondo is one of a number of scholars who have studied Mrs Okawa and other centenarians as they try to pin down more traits that identify those of us who will live the longest.

Those studies suggest that people with a strong will, are outgoing and a sense of curiosity live longer than average.

Mrs Okawa underlined the determined side of her character after suffering a fall at the age of 102 in which she broke her leg. After she returned to the nursing home from a stay in hospital, the staff found her doing leg squats as she held on to a hand rail in the hall.

When asked what she was doing, Mrs Okawa replied that she was making sure her body did not get out of shape.

On her birthday, TV crews and national media have been invited to the nursing home to record the birthday festivities.

“We will be having a cake, of course,” said Mr Okada. “But we will only be having three candles, one for each figure of her 116 years, because that many candles could be dangerous.”